Java GUI Programming

• GUI stands for Graphical User Interface

Key Terms and Definitions

• Swing is a Java GUI widget toolkit providing lightweight components prefixed with "J".
• AWT (Abstract Window Toolkit) is an older GUI toolkit with heavyweight components, suitable for simple GUIs.
• JFrame is a top-level container for creating the main window of a GUI application.
• JPanel is a container used to group and organize other components within a GUI.
• A Layout Manager arranges components in a container (e.g., FlowLayout, GridLayout, BorderLayout).
• The Color Class sets colors for GUI components using RGB values
• The Font Class sets fonts for text in GUI components.
• ImageIcon displays images in labels or buttons.

Java GUI API

• Component Classes are used to create user interface elements (e.g., JButton, JLabel, JTextField).
• Container Classes hold other components (e.g., JFrame, JPanel, JApplet).
• Helper Classes support GUI components (e.g., Graphics, Color, Font, FontMetrics, Dimension).

Container Classes

• JContainer groups components; Frames, panels, and applets are its subclasses.
• JFrame is a window that holds Swing components in Java GUI applications.
• JPanel is an invisible container that groups components and can be nested.
• JApplet is a subclass of Applet used to create Swing-based Java applets.
• JDialog is a popup window for receiving additional information or notifications.

GUI Helper Classes

• Helper classes reside in the java.awt package
• Graphics provides methods for drawing strings, lines, and shapes.
• Color manages colors for GUI components (e.g., background, foreground).
• Font specifies fonts for text (e.g., type, style, size).
• FontMetrics provides properties of fonts.
• Dimension encapsulates the width and height of a component.
• LayoutManager specifies how components are arranged in a container.

Frames

• A JFrame creates the main window for a GUI application.
• Each JFrame contains a content pane.
• GUI components are placed in the content frame.
• A content pane is an instance of JContainer
• To create a user interface, create either a frame or an applet to hold the user interface components.
• Steps to create a frame:
  • Create a JFrame object.
  • Set the frame size using setSize(width, height).
  • Center the frame using setLocationRelativeTo(null).
  • Set the default close operation using setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE).
  • Make the frame visible using setVisible(true).
• A pixel is the smallest unit of space available for drawing on the screen.
• Resolution specifies the number of pixels per square inch.

Layout Managers

• Layout managers automatically maps user interfaces on all window systems.
• Layout managers are set in containers using the setLayout(aLayoutManager) method.
• FlowLayout arranges components left to right, top to bottom.
  • Alignment options: FlowLayout.LEFT, CENTER, RIGHT.
  • Example: setLayout(new FlowLayout(FlowLayout.LEFT, 10, 20)).
• GridLayout arranges components in a grid (rows and columns).
  • Example: setLayout(new GridLayout(3, 2, 5, 5)).
• BorderLayout divides the container into five areas: NORTH, SOUTH, EAST, WEST, CENTER.
  • Example: add(new JButton("Center"), BorderLayout.CENTER).
• FlowLayout: has alignment, hgap, and vgap properties, settable via setAlignment, setHgap, and setVgap.
• GridLayout: has rows, columns, hgap, and vgap properties, settable via setRows, setColumns, setHgap, and setVgap.
• BorderLayout: has hgap and vgap properties, settable via setHgap and setVgap.

Using Panels as Subcontainers

• Panels group components within a frame or another panel.
• Panels act as subcontainers.
• Panels can be placed inside a frame or inside another panel.
• Java GUI can divide a window to panels.
• Swing’s panel is Jpanel
• new JPanel() creates a panel with a default FlowLayout manager.
• new JPanel(LayoutManager) creates a panel with the specified layout manager.
• Use the add(Component) method to add a component to the panel.
• Example:
  • Create a JPanel with a GridLayout for buttons.
  • Add the panel to the frame using add(panel, BorderLayout.CENTER).

Color Class

• Colors are defined using RGB values (0-255).
• An IllegalArgumentException occurs if a value beyond this range is passed to the argument.
• Set colors using java.awt.Color
• Example: Color color = new Color(128, 100, 100).
• Set background and foreground colors using setBackground(Color) and setForeground(Color) in java.awt.Component.
• Standard colors: BLACK, BLUE, CYAN, DARK_GRAY, GRAY, GREEN, LIGHT_GRAY, MAGENTA, ORANGE, PINK, RED, WHITE, YELLOW.

Font Class

• Create a font using Font(String name, int style, int size) from java.awt.Font
• Font name options: SansSerif, Serif, Monospaced, Dialog, or DialogInput.
• Style: Font.PLAIN (0), Font.BOLD (1), Font.ITALIC (2), and Font.BOLD + Font.ITALIC (3),
• Constructor: public Font(String name, int style, int size);
• GraphicsEnvironment is an abstract class that describes the graphics environment on a particular system
• Example: Font font = new Font("SansSerif", Font.BOLD, 16).
• Set fonts for components using setFont(Font).

ImageIcon

• Images are normally stored in image files
• An icon is a fixed-size picture used to decorate components
• Images are displayed in labels or buttons.
• Supported formats: GIF, JPEG, PNG.
• Example: ImageIcon icon = new ImageIcon("image/us.gif").
• An Image is displayed in a label with: JLabel label = new JLabel(icon).

Common Features of Swing GUI Components

• Public methods: Component, Container, and JComponent.
• Component class is the root for all GUI components and containers.
• All Swing GUI components are subclasses of JComponent, except JFrame, JApplet, and JDialog.
• You can set a border on any object of the JComponent class.
• Tool Tips: Text displayed when hovering over a component. jbtRight.setToolTipText("This is the Right button") provides an example.
• Borders: decoration for components. For Example: p1.setBorder(new TitledBorder("Three Buttons")).